Electroactive polymer transducers

ABSTRACT

Dielectric elastomer or electroactive polymer film transducers configured to minimize high electrical field gradients that can lead to partial discharge and corona.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 11/956,269, filed on Dec. 13, 2007, the content ofwhich is incorporated herein by reference in its entirety

FIELD OF THE INVENTION

The present invention relates to dielectric elastomer or electroactivepolymer film transducers and optimizing their performance by minimizinghigh electrical field gradients that can lead to partial discharge andcorona.

BACKGROUND OF THE INVENTION

A tremendous variety of devices used today rely on actuators of one sortor another to convert electrical energy to mechanical energy.Conversely, many power generation applications operate by convertingmechanical action into electrical energy. Employed to harvest mechanicalenergy in this fashion, the same type of actuator may be referred to asa generator. Likewise, when the structure is employed to convertphysical stimulus such as vibration or pressure into an electricalsignal for measurement purposes, it may be referred to as a sensor. Yet,the term “transducer” may be used to generically refer to any of thedevices.

A number of design considerations favor the selection and use ofadvanced dielectric elastomer materials, also referred to as“electroactive polymers” (EAPs), for the fabrication of transducers.These considerations include potential force, power density, powerconversion/consumption, size, weight, cost, response time, duty cycle,service requirements, environmental impact, etc. As such, in manyapplications, EAP technology offers an ideal replacement forpiezoelectric, shape-memory alloy (SMA) and electromagnetic devices suchas motors and solenoids.

An EAP transducer comprises two thin film electrodes having elasticcharacteristics and separated by a thin elastomeric dielectric material.When a voltage difference is applied to the electrodes, theoppositely-charged electrodes attract each other thereby compressing thepolymer dielectric layer therebetween. As the electrodes are pulledcloser together, the dielectric polymer film becomes thinner (the z-axiscomponent contracts) as it expands in the planar directions (the x- andy-axes components expand).

Examples of EAP devices and their applications are described in U.S.Pat. Nos. 7,394,282; 7,378,783; 7,368,862; 7,362,032; 7,320,457;7,259,503; 7,233,097; 7,224,106; 7,211,937; 7,199,501; 7,166,953;7,064,472; 7,062,055; 7,052,594; 7,049,732; 7,034,432; 6,940,221;6,911,764; 6,891,317; 6,882,086; 6,876,135; 6,812,624; 6,809,462;6,806,621; 6,781,284; 6,768,246; 6,707,236; 6,664,718; 6,628,040;6,586,859; 6,583,533; 6,545,384; 6,543,110; 6,376,971 and 6,343,129; andin U.S. Patent Application Publication Nos. 2008/0157631; 2008/0116764;2008/0022517; 2007/0230222; 2007/0200468; 2007/0200467; 2007/0200466;2007/0200457; 2007/0200454; 2007/0200453; 2007/0170822; 2006/0238079;2006/0208610; 2006/0208609; and 2005/0157893, the entireties of whichare incorporated herein by reference.

Many EAP transducer operate at high voltages, e.g., in the range fromabout 0.5 kV to about 50 kV. Like any high voltage device, EAPtransducers are susceptible to partial discharge. Energy moves from aregion of high electrical potential to a region of lower electricalpotential, e.g., from the high voltage electrode to the groundelectrode. A partial discharge occurs when a small quantity of charge(i.e., picoCoulombs) does not bridge the entire space between theelectrodes. Areas of steep gradients in electrical potential favorpartial discharges. These include electrode edges, projections extendingfrom an electrode, cracks internal to the electrode, and gas filledmicrovoids within the dielectric material. Generally, the smaller theradius of curvature of the electrode geometry, the lower the voltagenecessary to initiate and maintain partial discharge. Put another way,the smoother the electrode surfaces, the less likely partial dischargewill occur.

Partial discharges through air are particularly damaging to dielectricelastomer transducers. The discharge may be from the electrode into theair, which serves as a virtual ground—a phenomenon commonly called“corona discharge.” Alternately, the charge may pass though the air asit jumps from the electrode to an adjacent region of the dielectricsurface. In either case, movement of the charge through air isenergetic, producing fluorescence, ionized gas, and temperatures withinthe arc on the order of thousands of degrees Celsius. The ionized gasreacts to produce corrosive materials like ozone and nitrogen oxidesthat yield nitric acid under conditions of high humidity. These reactivespecies, in combination with the high temperatures present within theelectrical arc, erode the electrode and dielectric materials and canshorten the life span of a transducer.

The inventors of the subject invention are not aware of any prior artdielectric elastomer/electroactive polymer transducers that are designedto inhibit or suppress partial discharge and corona. Thus, it would behighly advantageous to fabricate and provide EAP transducers having sucha feature.

SUMMARY OF THE INVENTION

The present invention provides EAP films, transducer films andtransducers configured or designed to suppress or minimize partialdischarge, and methods of fabricating such transducers. These films arefabricated in part by coating or encapsulating at least a portion of thefilm with a partial discharge suppressant for a purpose of excluding airto minimize the corona effect and/or reducing the high concentration ofelectrical stress gradients and thereby minimize degradation of thedielectric by partial discharge.

Generally, the partial discharge suppressant or partial dischargesuppressing material, also referred to interchangeably herein as anencapsulent or coating, is placed in regions of the film having a steepelectrical gradient thereby distributing the electrical field andminimizing the electrical stress at one or more locations or regions ofthe film.

The subject films may be employed as transducers for application inactuators, generators, sensors, and the like, or as components thereof.

These and other features, objects and advantages of the invention willbecome apparent to those persons skilled in the art upon reading thedetails of the invention as more fully described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in conjunction with the accompanying schematic drawings, wherevariation of the invention from that shown in the figures iscontemplated. To facilitate understanding of the invention description,the same reference numerals have been used (where practical) todesignate similar elements that are common to the drawings. Wherecross-sectional views are provided (FIGS. 2B-7B), those views are takenalong the line B-B in corresponding top views (FIGS. 2A-7A). Included inthe drawings arc the following figures:

FIGS. 1A and 1B illustrate a top perspective view of a transducer beforeand after application of a voltage in accordance with one embodiment ofthe present invention;

FIGS. 2A and 2B are top and cross-sectional views, respectively, of anEAP film for use in the subject transducers having a partial dischargesuppressant covering the entirety of the exposed or outwardly facingportions of the electrodes and a portion of the dielectric elastomer;

FIGS. 3A and 3B are top and cross-sectional views, respectively, of anEAP film for use in the subject transducers having a partial dischargesuppressant covering the entirety of the exposed or outwardly facingportions of the electrodes and dielectric elastomer;

FIGS. 4A and 4B are top and cross-sectional views, respectively, of anEAP film for use in the subject transducers having a partial dischargesuppressant disposed between the dielectric material and the electrodes,thereby covering a substantial portion of both sides of the dielectricelastomer material;

FIGS. 5A and 5B are top and cross-sectional views, respectively, of anEAP film for use in the subject transducers with a partial dischargesuppressant covering the entirety of the exposed or outwardly facingsides of the electrodes and at least a minimal portion of the dielectricelastomer in order to bridge across the edges of the electrodes;

FIGS. 6A and 6B are top and cross-sectional views, respectively, of anEAP film for use in the subject transducers having a partial dischargesuppressant covering the entirety of the exposed or outwardly facingside of the top electrode and a portion of the top side of thedielectric elastomer but not any portion of the bottom side of the EAPfilm;

FIGS. 7A and 7B are top and cross-sectional views, respectively, of anEAP film for use in the subject transducers having a partial dischargesuppressant covering only the edges of the electrodes and a relativelysmall portion of both sides of the dielectric elastomer; and

FIG. 8 illustrates a process flow for fabricating an EAP transducerhaving a partial discharge suppressant in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Before describing particular embodiments of the materials, devices andsystems of the present invention, a discussion of compliantelectroactive capacitive structures and their material properties andperformance characteristics is provided.

FIGS. 1A and 1B illustrate a capacitive structure in the form of anelectroactive film or membrane 10. A thin elastomeric dielectric film orlayer 12 is sandwiched between compliant or stretchable electrode platesor layers 14 and 16, thereby forming a capacitive structure or film. Thelength “l” and width “w” of the dielectric layer, as well as that of thecomposite structure, are much greater than its thickness “t”. Typically,the dielectric, layer has a thickness in range from about 10 μm to about100 μm, with the total thickness of the structure in the range fromabout 25 μm to about 10 cm. Additionally, it is desirable if possible toselect the elastic modulus, thickness, and/or the microgeometry ofelectrodes 14, 16 such that the additional stiffness they contribute tothe actuator is generally less than the stiffness of the dielectriclayer 12, which has a relatively low modulus of elasticity, i.e., lessthan about 100 MPa and more typically less than about 10 MPa, but islikely thicker than each of the electrodes. Electrodes suitable for usewith these compliant capacitive structures are those capable ofwithstanding cyclic strains greater than 1% without failure due tomechanical fatigue.

As seen in FIG. 1B, when a voltage is applied across the electrodes, theunlike charges in the two electrodes 14, 16 are attracted to each otherand these electrostatic attractive forces compress the dielectric film12 (along the Z-axis). The dielectric film 12 is thereby caused todeflect with a change in electric field. As electrodes 14, 16 arecompliant, they change shape with dielectric layer 12. Generallyspeaking, deflection refers to any displacement, expansion, contraction,torsion, linear or area strain, or any other deformation of a portion ofdielectric film 12. Depending on the form fit architecture, e.g., aframe, in which capacitive structure 10 is employed (collectivelyreferred to as a “transducer”), this deflection may be used to producemechanical work. Various different transducer architectures aredisclosed and described in the above-identified patent references.

With a voltage applied, the transducer film 10 continues to deflectuntil mechanical forces balance the electrostatic forces driving thedeflection. The mechanical forces include elastic restoring forces ofthe dielectric layer 12, the compliance or stretching of the electrodes14, 16 and any external resistance provided by a device and/or loadcoupled to transducer 10. The resultant deflection of the transducer 10as a result of the applied voltage may also depend on a number of otherfactors such as the dielectric constant of the elastomeric material andits size and stiffness. Removal of the voltage difference and theinduced charge causes the reverse effects.

In some cases, the electrodes 14 and 16 may cover a limited portion ofdielectric film 12 relative to the total area of the film. This may bedone to prevent electrical breakdown around the edge of the dielectricor achieve customized deflections in certain portions thereof.Dielectric material outside an active area (the latter being a portionof the dielectric material having sufficient electrostatic force toenable deflection of that portion) may be caused to act as an externalspring force on the active area during deflection. More specifically,material outside the active area may resist active area deflection byits contraction or expansion.

The dielectric film 12 may be pre-strained. The pre-strain improvesconversion between electrical and mechanical energy, i.e., thepre-strain allows the dielectric film 12 to deflect more and providegreater mechanical work. Pre-strain of a film may be described as thechange in dimension in a direction after pre-straining relative to thedimension in that direction before pre-straining. The pre-strain maycomprise elastic deformation of the dielectric film and be formed, forexample, by stretching the film in tension and fixing one or more of theedges while stretched. The pre-strain may be imposed at the boundariesof the film using a rigid frame or may be implemented for only a portionof the film.

The transducer structure of FIGS. 1A and 1B and other similar compliantstructures and the details of their constructs are more fully describedin many of the above-referenced patents and publications.

The present invention provides EAP films, transducer films andtransducers configured or designed to suppress or minimize partialdischarge, and methods of fabricating such transducers. These EAPtransducers are fabricated in part by coating or encapsulating at leasta portion of the EAP film forming the transducer with a partialdischarge suppressant for a purpose of excluding air to minimize thecorona effect and thereby minimize degradation of the dielectric bypartial discharge.

Generally, the partial discharge suppressant or partial dischargesuppressing material, also referred to interchangeably herein as anencapsulent or coating, is placed in regions of the film having a steepelectrical gradient, e.g., at the edges of the electrode material,thereby distributing the electrical field and minimizing the electricalstress at one or more locations or regions of the film. The suppressantmaterial may cover the entirety of the electrodes forming the EAP filmor portions thereof, e.g., just the edges of the electrode material. Thesuppressant material may be provided as an outer layer on one or bothsides of the EAP film, or may be interposed between the electrodes andthe dielectric material. Additionally, the coating or encapsulationmaterial may cover the entirety or a portion of the dielectric materialforming the EAP film. Alternatively, the coating or encapsulation maycover dielectric material only and not any portion of the electrodes.Still yet, the entirety of the electrode and dielectric materials may becoated with the suppressant material. Optionally, coatings, particularlythose having a high dielectric breakdown strength, may be partiallyimpregnated into the dielectric and/or electrode materials, for exampleby migration of a transformer-grade dielectric oil from the encapsulantinto the underlying dielectric.

FIGS. 2-7 illustrate variety of exemplary configurations of EAPtransducer films designed for partial discharge suppression wherein apartial discharge suppressing material, encapsulent or conformal coatingis applied to the EAP film according to the present invention. The EAPfilm of each of these figures includes a dielectric elastomer layer 22disposed between top and bottom electrodes 24 a, 24 b. Theencapsulent/coating covers at least a portion of the actuating surfaceof one or both electrodes and/or the edges of the electrode material.Each electrode has a radially extending tab 26 (viewable from therespective top views) which is not encapsulated or coated in order toenable electrical connection of the transducer to a power supply (notillustrated). For clarity of illustration, the frame members that holdthe transducer EAP films are not illustrated in the figures.

FIGS. 2A and 2B illustrate a transducer film 20 encapsulated/coated onboth sides with encapsulent/coating 28 a, 28 b. The encapsulant materialcovers the entirety of the exposed or outwardly facing electrodesurfaces 24 a, 24 b (except for the electrode tabs 26) and a portion ofboth sides of dielectric elastomer 22, i.e., the encapsulent provides apartial outer layer on both sides of the transducer film. Fullencapsulation is suitable for suppressing partial discharges at theelectrode edges, and also suppressing discharges which may occur atimperfections within the body of the electrode (e.g., at cracks, pits,inclusions of dust, etc.). Furthermore, a full coating provides someprotection to electrodes that are vulnerable to corrosion in air (e.g.,thin film metals), and provides a layer of electrical insulation that,if adequately thick and robust, may make the device suitable for directhuman contact in the absence of other packaging.

FIGS. 3A and 3B illustrate a transducer film 30 with the entirety ofboth electrodes 24 a, 24 b and the entirety of both sides of dielectricelastomer 22 encapsulated/coated with encapsulent/coating 38 a, 38 b,i.e., the encapsulent provides a complete outer layer over thetransducer film. This variation provides the potential added benefit ofhermetically sealing the transducer.

FIGS. 4A and 4B illustrate a transducer film 40 with a substantialportion of both sides of dielectric elastomer 22 covered byencapsulant/coating 48 a, 48 b without any exposed or outwardly facingportion of the electrodes 24 a, 24 b being encapsulated or coated.Rather, a primer layer of encapsulant lies between one or bothelectrodes, i.e., is in contact with the inwardly facing side of theelectrodes, and a surface of the dielectric layer. Optionally, a layerof encapsulant/coating may also be applied on top of the electrodematerial on one or both sides of film 40. This configuration has thebenefit of making the dielectric surface more uniform. This may beaccomplished by first dipping the dielectric layer in the coating priorto adding the electrode material and, optionally, a top layer ofcoating. If the primer layer is sufficiently thin, (e.g., aboutone-tenth of the dielectric thickness), then it can be stiffer than thedielectric, thus acting as a mechanical stress grading between the softdielectric and relatively stiffer electrode. A mechanical stress gradingcan be useful for metal electrodes, since it spatially low-pass filtersstress concentrations that can crack the metal. Alternately, if theprimer layer is a material with good stress grading properties, i.e.,having a dielectric constant greater than about 3 and having aresistivity in the range of about 1E6 to about 1E13 ohm·m, then it canserve the function of an electrical stress grading.

FIGS. 5A and 5B illustrate a transducer film 50 with the entirety of theelectrodes 24 a, 24 b encapsulated/coated with partial dischargesuppressant 58 a, 58 b and at least a minimal portion of the dielectricelastomer 22 in order to bridge across the edges of the electrodes. Thisvariation is well-suited for encapsulents which tend to migrate andinterfere with adhesion of rigid components to the dielectric, e.g.,encapsulents containing oil. An encapsulate-free zone between the activeregion and stiffening components on the device perimeter insuresadequate adhesion of other components, for example a frame (not picturedin the diagram), that is attached away from the encapsulated area,beyond the area affected by oil migration.

FIGS. 6A and 6B 5B illustrate a transducer film 60 with the entirety ofthe outward-facing side of top electrode 24 a and a portion of the topside of the dielectric elastomer 22 being encapsulated/coated withpartial discharge suppressant 68 without any portion of the bottom sideof the EAP film being encapsulated or coated. While theunencapsulated/uncoated side of the EAP film may be subject to partialdischarge, encapsulating/coating only one side of the EAP film is easierthan encapsulating/coating both sides, requiring fewer steps and lesstime. Additionally, a one-sided encapsulated film is less likely to haveits compliancy and flexibility inhibited.

FIGS. 7A and 7B 5B illustrate a transducer film 70 with only the edgesof the electrodes 24 a, 24 b encapsulated/coated with partial dischargesuppressant 78 a, 78 b and only a minimal portion of the exposeddielectric elastomer 22 being encapsulated/coated. This design adds noparasitic stiffness to most of the active area, but does suppresspartial discharges at the electrode edge. This approach is suitable forelectrodes that are relatively free of imperfections within the activearea.

In other embodiments of the subject transducer films, the EAP filmprovides more than one active area or a plurality of active areas whereeach active area has at least two electrodes on a dielectric elastomer.Each active area either deflects in response to a change in electricfield provided by the electrodes of the respective active area or causesa change in electric field in response to deflection of the respectiveactive area. In these transducer embodiments, one or more of the activeareas may also employ an encapsulate material in anyelectrode-dielectric-encapsulate arrangement or configuration of thepresent invention.

Because EAP transducers films are highly compliant and stretchable, thecoating/encapsulation material must be compliant as well, i.e., have aminimum linear strain greater than about 5%, and add relatively littlestiffness to the electroactive polymer film such that the displacementof the transducer diaphragm is not impeded. As such, the encapsulentmaterial, when coated at the desired thickness, should have a springconstant at least as low as that of the dielectric. A low modulusencapsulant adds little stiffness, even when coated as a relativelythick layer, facilitating defect-free manufacturing. To this end, it isdesirable to use an encapsulant with an elastic modulus at least as lowas that of the dielectric material. In many applications, the elasticmodulus of the coating is typically less than about 1 MPa, e.g., a PDMSgel with low cross linking. In applications where the desired mechanicalresponse is primarily viscous, the coating essentially has an elasticmodulus of zero, e.g., high molecular weight PDMS grease.

Suitable coating/encapsulation materials for the present inventioninclude but are not limited to low-modulus solids, viscoelastic gels,and dielectric liquids, optionally filled with particulates that raisedielectric constant and/or lower resistivity. Examples of suitable lowmodulus solids include poly(dimethylsiloxane) (PDMS),styrene-ethylene/butylene-styrene block copolymer (SEBS), polyurethane(PU), poly(n-butyl acrylate), poly(isobutene). The modulus of thesesolids can be lowered further by reducing the cross link density, or byadding a compatible dielectric liquid to form a viscoelastic gel.Suitable dielectric liquids include, for example, PDMS oils and mineraloils. It is also possible to use a completely un-crosslinked dielectricliquid when it is sufficiently viscous (e.g., long-chain PDMS grease),or is filled with enough particulates to make a paste.

Even without the addition of any fillers, the partial dischargesuppressant comprised of polymer and/or dielectric liquid will have adielectric constant (∈) greater than that of air (∈_(AIR)=≅1.0). Highdielectric constant is desirable, because raising the dielectricconstant of material near the electrode edge makes the gradient in theelectric field less steep, thus reducing the tendency of charge to jumpfrom the electrode. Unfilled polymers typically have dielectricconstants=≅2.5 to 4.5), whereas filled polymers can have dielectricconstants=≅5 to 200). The coating also preferably has a resistivity inthe range of semiconducting to insulating, or about 1E5 to about 1E14Ω·m. The dielectric constant of the coating material may be raised, forexample, by incorporating particles of a material with higher dielectricconstant such as titanium dioxide, barium titanate, zinc oxide, aluminumoxide, silicon carbide, etc. In a similar way, the conductivity of thesubstantially non-conductive coating can be raised to a desired value bythe addition of particles that are conducting, (e.g., carbon black,nanotubes, PEDOT, PANI, metal flakes, etc.) or semiconducting, (e.g.,silicon, silicon carbide, etc.).

In some constructions, particularly those in which subsequent packagingof the EAP transducer substantially retards ingress of water vapor andoxygen, it is desirable to add fillers to the encapsulant layer tosequester water vapor or oxygen that remains in the package afterassembly. Suitable fillers for scavenging water vapor include molecularsieves 4A, silica gel, montmorillonite clay, zeolites etc. Suitablefillers for scavenging oxygen include, for instance, Fe powder, sodiumsulfite, butylated hydroxytoluene, and butylated hydroxyanisole.

The processes and techniques for fabricating the subject EAP films andtransducers may vary greatly given the broad range of transducer designsand applications, with a wide range of electrode, dielectric and partialdischarge suppressing materials to choose from.

The transducers of the present invention may be fabricated in whole orin part by batch processing and/or continuous web fabrication techniquesby which the transducers are provided individually or in a planar array.FIG. 8 illustrates a process flow 80 for fabricating an EAP devicehaving at least one dielectric elastomer layer in accordance with onefabrication method of the present invention. Processes in accordancewith the present invention may include up to several additional stepsnot described or illustrated herein. In some cases, fabricationprocesses of the present invention may include conventional materialsand techniques such as commercially available dielectric elastomer andelectrode materials as well as techniques used in fabrication ofmicroelectronics and electronics technologies.

The process flow 80 begins by providing, receiving or fabricating adielectric elastomer (82). The dielectric elastomer may be provided orfabricated according to several methods. In one embodiment, thedielectric elastomer is a commercially available product such as acommercially available silicone or acrylic elastomer film. In otherembodiments, the dielectric elastomer is a film produced by coating,casting, dipping or spraying techniques. Roll-to-roll or web-basedcoating, for example, involves forming a layer of uncured polymer on arigid carrier coated with a release agent. Typical coating processes(e.g., reverse roll, knife, slot-die, curtain, etc.) produce films inthe range of about 10 to about 100 microns thick, which are cured bypassage through a tunnel oven. The polymer film may then be released bymechanical peeling. Preferably, the dielectric elastomer is producedwhile minimizing variations in thickness or any other defects that maycompromise the maximum electric field that can be applied across thedielectric elastomer and thus compromise performance.

As mentioned previously, the dielectric material may be pre-strained inone or more directions (84). In one embodiment, pre-strain is achievedby mechanically stretching a polymer in or more directions and fixing itto one or more solid members (e.g., rigid plates) while strained.Another technique for maintaining pre-strain includes the use of one ormore stiffeners. The stiffeners arc long rigid structures placed on apolymer while it is in a stretched state. The stiffeners maintain thepre-strain along their axis. The stiffeners may be arranged in parallelor other configurations to achieve directional compliance of thetransducer. It should be noted that the increased stiffness along thestiffener axis comprises the increased stiffness provided by thestiffener material as well as the increased stiffness of the polymer inthe pre-strain direction.

Surfaces on the pre-strained dielectric material may be textured toprovide directional compliance of the material. In general, a texturedsurface may comprise any uniform (e.g., corrugated) or non-uniform(e.g., roughened) surface topography that allows a polymer to deflect inthe desired direction. One manner of providing texturing is to stretchthe polymer material more than it can stretch when actuated and thendepositing a thin layer of stiff material on the stretched polymersurface. The stiff material, for example, may be a polymer which iscured after deposition. Upon relaxing, the composite structure bucklesto provide the textured surface. The thickness of the stiff material maybe altered to provide texturing on any scale, including submicrometerlevels. In another embodiment, textured surfaces are produced byreactive ion etching (RIE).

In certain transducer film embodiments it is desirable to provide aprimer layer of partial discharge suppressant, such as the filmembodiment of FIGS. 4A and 4B. With these embodiments, the partialdischarge suppressant is deposited (86) prior to providing the electrodematerial (88). If no primer layer is used, then one or more electrodesare formed directly on the dielectric material (88). If the dielectrichas been textured or corrugated, one or more thin layers of suitablemetal (e.g., chromium, aluminum, indium, tin, silver, gold, etc.) may besputter deposited on the surface to provide a textured electrode. Inanother embodiment, carbon-filled electrodes may be patterned anddeposited using a suitable process such as stenciling, screen-printing,pad-printing, flexographic printing, etc.

For transducer film embodiments such as those of FIGS. 2A/B, 3A/B, 5A/B,6A/B and 7A/B, a layer of partial discharge suppressant is thendeposited over a portion or substantially the entire electroactivepolymer surface (88), except for the electrode contact(s) 26. Suitablesuppressant application/coating methods include but are not limited tostenciling, spraying, dip-coating, screen-printing, pad-printing,flexographic printing, knife-overcoating, meter-rod coating, etc.,followed by a curing step. To minimize voids in the encapsulent, it isdesirable to de-gas the encapsulent before coating, and to apply it in away that minimizes entrapped air.

Rigid frames, rigid members or other electrical and mechanicalconnectors, depending on the transducer application, are attached to theEAP film either before or after deposition of the electrode material toform the transducer structure (step not illustrated). The transducer,comprising one or more EAP film layers, is then packaged or configuredwithin a selected form factor (90), e.g., for operation as an actuator,generator, sensor, etc. Packaging may also include assembly of multipletransducers mechanically linked or stacked as multiple layers. Packagingmay also include assembly of a barrier layer that encloses thetransducers in a space with an inert atmosphere (e.g., N₂, SF₆, He, Ne,Ar), or include a desiccant air that has been modified by incorporatinga particulate solid, i.e., desiccant, within the package or within theencapsulant itself. Such desiccant materials may comprise a chemicallyreactive complexing agent such as Fe powder for O₂ scavenging, silicafor H₂O scavenging, etc. The material may be a molecular sieve orzeolite. Alternatively, included particulate may be a blowing agent,such as Calogen or Safoam that generates CO₂ (see, e.g., U.S. Pat. No.7,314,895, incorporated herein by reference), N₂, or other gases),and/or humidity buffers such as acrylamide gels (see, e.g., WO1991/000316, incorporated herein by reference).

Although fabrication of subject EAP transducers and transducer films hasbeen briefly described with respect to a few specific examples,fabrication processes and techniques of the present invention may varyaccordingly for any the actuators or applications described above. Forexample, the process for fabricating a diaphragm actuator in accordancewith a specific embodiment may include adding some stiffening packagingcomponents before formation of the electrode (86). Likewise, depositionof the metal electrode in a stretched state may provide a corrugatedtexture to the dielectric/electrode interface, so that steps (84) and(86) are combined.

As for other details of the present invention, materials and alternaterelated configurations may be employed as within the level of those withskill in the relevant art. The same may hold true with respect tomethod-based aspects of the invention in terms of additional acts ascommonly or logically employed. In addition, though the invention hasbeen described in reference to several examples, optionallyincorporating various features, the invention is not to be limited tothat which is described or indicated as contemplated with respect toeach variation of the invention. Various changes may be made to theinvention described and equivalents (whether recited herein or notincluded for the sake of some brevity) may be substituted withoutdeparting from the true spirit and scope of the invention. Any number ofthe individual parts or subassemblies shown may be integrated in theirdesign. Such changes or others may be undertaken or guided by theprinciples of design for assembly.

Also, it is contemplated that any optional feature of the inventivevariations described may be set forth and claimed independently, or incombination with any one or more of the features described herein.Reference to a singular item, includes the possibility that there areplural of the same items present. More specifically, as used herein andin the appended claims, the singular forms “a,” “an,” “said,” and “the”include plural referents unless the specifically stated otherwise. Inother words, use of the articles allow for “at least one” of the subjectitem in the description above as well as the claims below. It is furthernoted that the claims may be drafted to exclude any optional element. Assuch, this statement is intended to serve as antecedent basis for use ofsuch exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Without the use of such exclusive terminology, the term“comprising” in the claims shall allow for the inclusion of anyadditional element—irrespective of whether a given number of elementsare enumerated in the claim, or the addition of a feature could beregarded as transforming the nature of an element set forth n theclaims. For example, adding a fastener or boss, complex surface geometryor another feature to a “transducer” as presented in the claims shallnot avoid the claim term from reading on accused structure. Statedotherwise, unless specifically defined herein, all technical andscientific terms used herein are to be given as broad a commonlyunderstood meaning as possible while maintaining claim validity.

In all, the breadth of the present invention is not to be limited by theexamples provided. That being said, we claim:

1-17. (canceled)
 18. A method of fabricating the transducer filmcomprising the steps of: providing the dielectric elastomer material,forming one or more electrodes are then formed on the dielectricelastomer material and forming a layer of partial discharge suppressantover at least a portion of at least one of the dielectric elastomermaterial or the electrode material wherein the partial dischargesuppressant has a dielectric constant greater than that of air and amodulus of elasticity no greater than that of the dielectric elastomer.19. The method of claim 18, wherein the layer of partial dischargesuppressant is formed prior to forming the one or more electrodes. 20.The method of claim 18, wherein the partial discharge suppressant isformed by one of stenciling, spraying, dip-coating, screen-printing,pad-printing, flexographic printing, knife-overcoating and meter-rodcoating.
 21. The method of claim 18, wherein at least some steps of themethod are performed by web-based fabrication techniques.
 22. A methodof packaging the transducer film of claim 18, the method comprisingenclosing the transducer film to provide an inert atmosphere.
 23. Amethod of packaging the transducer film of claim 18, the methodcomprising enclosing the transducer film within air that has beenmodified by incorporating a chemically reactive solid therein.